Method and apparatus for relaying data in wireless communication system based on tdd

ABSTRACT

The present invention provides a method and an apparatus of relaying data in a wireless communication system based on Time Division Duplex (TDD). A relay station receives downlink data from a base station in an uplink subframe and relays the downlink data to at least one mobile station. Accordingly, the efficiency of resource allocation for a relay station can be improved.

TECHNICAL FIELD

The present invention relates to wireless communication, and moreparticularly, to a method and an apparatus of relaying data in awireless communication system based on Time Division Duplex (TDD).

BACKGROUND ART

Methods for wireless communication systems may be chiefly classifiedinto a TDD method and a Frequency Division Duplex (FDD) method. Inaccordance with the FDD method, uplink transmission and downlinktransmission are carried out with them occupying different frequencybands. In accordance with the TDD method, uplink transmission anddownlink transmission are carried out with them occupying the samefrequency band at different times. The channel response of the TDDmethod is substantially reciprocal. It means that a downlink channelresponse and an uplink channel response are almost identical with eachother in a certain frequency domain. Accordingly, there is an advantagein that in a wireless communication system based on TDD, the downlinkchannel response can be obtained from the uplink channel response.

In the TDD method, downlink transmission by a base station (BS) anduplink transmission by a mobile station (MS) cannot be performed at thesame time because all the frequency bands are time-divided for uplinktransmission and downlink transmission. In a TDD system in which uplinktransmission and downlink transmission are classified on a subframebasis, uplink transmission and downlink transmission are carried out atdifferent subframes.

Recently, wireless communication systems including a relay station (RS)are being developed. The relay station functions to expand the cellcoverage and improve transmission performance. There is an advantage inthat the cell coverage can be expanded because a base station providesservice to a mobile station placed at the coverage edge of a basestation via the relay station. Further, the transmission capacity can beincreased because the relay station improves transmission reliability ofa signal between the base station and the mobile station. In the casewhere a mobile station is placed within the coverage of a base station,but placed in a shadow region, a relay station may be used.

The relay station is difficult to send data to a mobile station whilereceiving data from a base station. Further, the relay station isdifficult to send data to a base station while receiving data from amobile station. This is because a signal outputted from the transmissionstage of the relay station may interfere with a signal that should bereceived by the relay station under the influence of self-interference,distorting the signal.

In the wireless communication system based on TDD, uplink transmissionand downlink transmission cannot be performed at the same time.Accordingly, the wireless communication system based on TDD can havelower resource efficiency in the time domain than a wirelesscommunication system based on FDD. Furthermore, if a relay station isused in the wireless communication system based on TDD, radio resourcesmust be allocated to the relay station. As described above, the relaystation cannot perform the reception of data from a base station and thetransmission of data to a mobile station (or the transmission of data tothe base station and the reception of data to the mobile station) at thesame time. Thus, the efficiency of resource allocation in the TDD systemcan be further lowered.

Accordingly, there is a need for a method of a relay station efficientlyrelaying data in a wireless communication system based on TDD.

DISCLOSURE OF INVENTION Technical Problem

Accordingly, the present invention has been made in view of the aboveproblems, and it is an object of the present invention to provide amethod and an apparatus of relaying data in a wireless communicationsystem based on TDD.

Solution to Problem

In an aspect, a method of relaying data in a wireless communicationsystem based on Time Division Duplex (TDD) using a radio framecomprising a plurality of subframes, the plurality of subframescomprising at least one downlink subframe and at least one uplinksubframe is provided. The method includes receiving downlink data from abase station in an uplink subframe, and relaying the downlink data to atleast one mobile station. The method may further include receivinguplink data from a mobile station in the uplink subframe. Resources usedby the base station to transmit the downlink data in the uplink subframeand resources used by the mobile station to transmit the uplink data maynot overlap with each other. The resources may be subject to timedivision or frequency division. The method may further include receivinginformation about the uplink subframe in which the downlink data isreceived. The method may further include selecting the uplink subframein which the downlink data is received among the plurality of uplinksubframes. The radio frame may comprise 10 subframes.

In another aspect, a relay station in a wireless communication systembased on TDD using a radio frame comprising a plurality of subframes,the plurality of subframes comprising at least one downlink subframe andat least one uplink subframe is provided. The relay station includes atransceiver configured to transmit or receive a radio signal, and aprocessor coupled to the transceiver and configured to process downlinkdata received from a base station and relay the downlink data to amobile station, wherein the processor receives the downlink data fromthe base station in at least any one of the uplink subframes included inthe radio frame.

Advantageous Effects of Invention

In a wireless communication system based on TDD in which uplinktransmission and downlink transmission are carried out on a subframebasis, data can be relayed without additional resource allocation for arelay station. Accordingly, efficiency of resource allocation can beincreased. Further, in a wireless communication system based on TDD, anew resource allocation is proposed for the operation of a relaystation.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a wireless communication system.

FIG. 2 is a diagram showing a wireless communication system using relaystations.

FIG. 3 is a diagram showing a TDD radio frame structure in a 3rdGeneration Partnership Project (3GPP) Long Term Evolution (LTE) system.

FIG. 4 is a diagram showing an example of data relay among a basestation, a relay station, and a mobile station in the uplink-downlinkconfiguration 1 of Table 1.

FIG. 5 is a diagram showing a data relay method according to anembodiment of the present invention.

FIG. 6 is a diagram showing the transmission of data in a downlinksubframe.

FIG. 7 is a diagram showing an example of the transmission of data in anuplink subframe.

FIG. 8 is a diagram showing another example of the transmission of datain an uplink subframe.

FIG. 9 is a diagram showing the transmission of data in a swappedsubframe.

FIG. 10 is a diagram showing the data relay method according to theembodiment of the present invention in the uplink-downlink configuration0.

FIG. 11 is a diagram showing the data relay method according to theembodiment of the present invention in the uplink-downlink configuration2.

FIG. 12 is a diagram showing the data relay method according to theembodiment of the present invention in the uplink-downlink configuration3.

FIG. 13 is a diagram showing the data relay method according to theembodiment of the present invention in the uplink-downlink configuration4.

FIG. 14 is a diagram showing the data relay method according to theembodiment of the present invention in the uplink-downlink configuration5.

FIG. 15 is a diagram showing the data relay method according to theembodiment of the present invention in the uplink-downlink configuration6.

FIG. 16 is a block diagram of a relay station according to an embodimentof the present invention.

MODE FOR THE INVENTION

Wideband Code Division Multiple Access (WCDMA) can be implemented usingradio technologies, such as Universal Terrestrial Radio Access Network(UTRAN) according to the 3GPP standards. CDMA2000 is CDMA-based radiotechnology. High Rate Packet Data (HRPD) in accordance with 3GPP2standards provides high packet data services in CDMA2000-based systems.Evolved HRPD (eHRPD) is the evolution of HRPD. Time Division MultipleAccess (TDMA) can be implemented using radio technologies, such asGlobal System for Mobile communications (GSM), General Packet RadioService (GPRS), and Enhanced Data rates for GSM Evolution (EDGE).Orthogonal Frequency Division Multiple Access (OFDMA) can be implementedusing radio technologies, such as IEEE 802.11 (Wi-Fi), IEEE 802.16(WiMAX), IEEE 802-20, and Evolved-UTRAN (E-UTRAN). Long Term Evolution(LTE) is part of Evolved-UMTS (E-UMTS) using E-UTRAN. LTE adopts OFDMAin the downlink and adopts Single Carrier FDMA (SC-FDMA) in the uplink.LTE-Advanced (LTE-A) is the evolution of LTE.

Although 3GPP LTE and LTE-A are chiefly described in order to clarify adescription, the technical spirit of the present invention is notlimited to the 3GPP LTE/LTE-A.

FIG. 1 shows a wireless communication system. The wireless communicationsystem 10 includes at least one base station (BS) 11. The base stations11 provide communication services to respective geographical areas (ingeneral called ‘cells’) 15 a, 15 b, and 15 c. Each of the cells can besubdivided into a number of areas (called ‘sectors’). One or more cellscan exist in a single base station.

A mobile station (MS) 12 can be fixed or mobile and can be referred toas another terminology, such as a User Equipment (UE), a User Terminal(UT), a Subscriber Station (SS), a wireless device, a Personal DigitalAssistant (PDA), a wireless modem, a handheld device, or an AccessTerminal (AT). In general, the base station 11 refers to a fixed stationwhich communicates with the mobile station 12. The base station 11 canbe referred to as another terminology, such as an evolved-NodeB (eNB), aBase Transceiver System (BTS), an access point, or an Access Network(AN).

Hereinafter, downlink (DL) refers to communication from a BS to an UE,and uplink (UL) refers to communication from a mobile station to a basestation. In the downlink, a transmitter can be part of a base stationand a receiver may be part of a mobile station. In the uplink, atransmitter can be part of a mobile station and a receiver can be partof a base station.

FIG. 2 shows a wireless communication system using relay stations. Inuplink transmission, a source station can be a mobile station, and adestination station can be a base station. In downlink transmission, asource station can be a base station and a destination station can be amobile station. A relay station may be a mobile station, and anadditional relay station can be deployed. A base station can performfunctions, such as connectivity, management, control, and resourceallocation between a relay station and a mobile station.

Referring to FIG. 2, a destination station 20 communicates with a sourcestation 30 via a relay station 25. In uplink transmission, the sourcestation 30 transmits uplink data to the destination station 20 and therelay station 25, and the relay station 25 transmits the received dataagain. Further, the destination station 20 communicates with a sourcestation 31 via relay stations 26 and 27. In uplink transmission, thesource station 31 transmits uplink data to the destination station 20and the relay stations 26 and 27, and the relay stations 26 and 27transmit the received data again sequentially or at the same time.

Although one destination station 20, three relay stations 25, 26, and27, and two source stations 30 and 31 are illustrated, the technicalspirit of the present invention is not limited to the above example. Itis to be noted that the number of destination stations, relay stationsand source stations included in a wireless communication system is notlimited.

Any method, such as Amplify and Forward (AF) and Decode and Forward(DF), can be used as a relay method for a relay station. The technicalspirit of the present invention is not limited to the methods.

FIG. 3 shows a TDD radio frame structure in the 3GPP LTE system. For theTDD radio frame structure, reference can be made to Paragraph 4.2 of3GPP TS 36.211 V8.2.0 (2008-03) “Technical Specification Group RadioAccess Network; Evolved Universal Terrestrial Radio Access (E-UTRA);Physical Channels and Modulation (Release 8)”. A single radio frame is10 ms in length and is composed of two half-frames each having a lengthof 5 ms. Further, a single half-frame is composed of five subframes eachhaving a length of 1 ms. One subframe is designated as any one of anuplink (UL) subframe, a downlink (DL) subframe, and a special subframe.One radio frame includes at least one uplink subframe and at least onedownlink subframe.

The special subframe is a specific period for separating the uplink andthe downlink between an uplink subframe and a downlink subframe. Atleast one special subframe exists in one radio frame. The specialsubframe includes a Downlink Pilot Time Slot (DwPTS), a Guard Period(GP), and Uplink Pilot Time Slot (UpPTS). The DwPTS is used for initialcell search, synchronization, or channel estimation. The UpPTS is usedfor channel estimation in a base station and is used for upwardtransmission synchronization in a mobile station. The GP is a guardinterval for removing interference that occurs in the uplink because ofthe multi-path delay of a downlink signal between the uplink and thedownlink.

Table 1 below shows the structure of frames that can be set according tothe deployment of uplink subframes and downlink subframes in the 3GPPLTE TDD system. In this table, ‘D’ denotes the downlink subframe, ‘U’denotes the uplink subframe, and ‘S’ denotes the special subframe.

TABLE 1 UPLINK- DOWNLINK-TO-UPLINK DOWNLINK SWITCHING-POINT SUBFRAMENUMBER CONFIGURATION PERIODICITY 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U DS U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  DS U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D D DD D 6 5 ms D S U U U D S U U D

In Table, each of the uplink-downlink configurations 0 to 2 or 6 has aswitching point period of 5 ms and is a configuration in which theuplink and the downlink are switched. Each of the uplink-downlinkconfigurations 3 to 5 has a switching point period of 10 ms and is aconfiguration in which the uplink and the downlink are switched.

FIG. 4 is a diagram showing an example of data relay among a basestation, a relay station, and a mobile station in the uplink-downlinkconfiguration 1 of Table 1. At step S110, in an uplink subframe #2, arelay station receives data transmitted by a mobile station. At stepS120, in an uplink subframe #3, the relay station relays the data to abase station. At this time, the relay station cannot receive datatransmitted by the mobile station. Accordingly, the uplink subframe #3becomes a blank subframe from a viewpoint of the mobile station. Theblank subframe refers to a subframe to or from which any data is nottransmitted or received. The base station (or relay station) candesignate at least one of uplink subframes as a blank subframe using amethod of not performing uplink scheduling for the mobile station.Alternatively, the relay station may designate at least one of downlinksubframes as a blank subframe using a method of previously informing themobile station that any transmission will not be performed in acorresponding subframe. When the mobile station has the blank subframe,the relay station can communicate with the base station withoutinterference of the mobile station.

At step S130, in a downlink subframe #4, the relay station receives datatransmitted by the base station. At this time, the relay station cannottransmit data to the mobile station connected to the relay station. Thedownlink subframe #4 becomes a blank subframe from a viewpoint of themobile station.

Since the uplink-downlink configuration 1 has the switching point periodof 5 ms, subframes #5 to #9 have the same shape as the respectivesubframes #0 to #4. Accordingly, at step S140, in the uplink subframe#7, the relay station receives data transmitted by the mobile station.At step S150, in the uplink subframe #8, the relay station relays thedata to the base station. The uplink subframe #8 becomes a blanksubframe from a viewpoint of the mobile station. At step S160, in thedownlink subframe #9, the relay station receives data transmitted by thebase station. The downlink subframe #9 becomes a blank subframe from aviewpoint of the mobile station.

In the case where a relay station and a base station transmit or receivedata using a blank subframe, a problem arises in terms of efficiency.Any data is not transmitted or received in the blank subframe. Thus,when a mobile station has a blank subframe, the mobile station is in astandby state in which any data is not transmitted or received. This maycause transmission delay or reduce a transmission capacity. Further, achange in the traffic between the base station and the relay station maynot be rapidly dealt with because the uplink-downlink configuration of ablank subframe is rarely changed.

FIG. 5 is a diagram showing a data relay method according to anembodiment of the present invention. A proposed structure adopts aswapped subframe in order to increase the efficiency of resourceallocation. In an original TDD uplink-downlink configuration, a basestation designates the swapped subframe as an uplink subframe for uplinktransmission to a mobile station. However, at least one of uplinksubframes is designated as the swapped subframe through dynamicallocation or static allocation, and a base station uses the swappedsubframe to transmit data to a relay station. The base station may usepart of or all the swapped subframe to transmit data to the relaystation. The swapped subframe is named in that an original use of anuplink subframe is swapped and may also be referred to as a stolensubframe.

At step S210, in an uplink subframe #2, a relay station transmits datato a base station. At this time, the relay station cannot receive datatransmitted by mobile stations. This can be implemented in such a mannerthat the relay station does not perform uplink scheduling for the mobilestations. At step S220, in an uplink subframe #3, the relay stationreceives data transmitted by the mobile stations according to anoriginal uplink-downlink configuration. At the same time, the relaystation receives data transmitted by the base station. In this case, anuplink subframe becomes a swapped subframe. In the uplink subframe #3(i.e., swapped subframe), the relay station receives data from themobile stations and the base station at the same time. The data receivedfrom the mobile stations and the data received from the base station maydiffer. The data received from the mobile stations and the data receivedfrom the base station can be transmitted through different resources.

At step S230, in a downlink subframe #4, the relay station relays thedata, received from the base station, to the mobile stations.

In a similar way, at step S240, in an uplink subframe #7, the relaystation transmits data to the base station. At step S250, an uplinksubframe #8 becomes a swapped subframe, and the relay station receivesuplink data from the mobile stations and downlink data from the basestation. At step S260, in a downlink subframe #9, the relay stationrelays the downlink data to the mobile stations.

As described above, in an uplink subframe (i.e., swapped subframe), therelay station receives downlink data from the base station. The downlinkdata is relayed to the mobile stations in a next downlink subframe.Accordingly, a blank subframe need not to be specially designated, andthe efficiency of resource allocation can be improved. Furthermore,transmission delay resulting from blank subframes can be prevented.

Although the uplink subframes #3 and #8 of the uplink subframes areillustrated to be the swapped subframes in FIG. 5, the technical spiritof the present invention is not limited to the above example. Forexample, the position or number of uplink subframes used as swappedsubframes can be fixed or changed. The position or number of uplinksubframes exchanged with swapped subframes may be determined between abase station and a relay station prior to the actual data transmission.Further, a base station may inform a relay station of information aboutan uplink subframe exchanged with a swapped subframe. A base station mayinform a relay station of information about a swapped subframe in theform of part of an RRC message, L1/L2 signaling, and system information.

FIG. 6 shows the transmission of data in a downlink subframe. A basestation 50 transmits first data to a first mobile station 52, and arelay station 51 relays second data to a second mobile station 53.

FIG. 7 is a diagram showing an example of the transmission of data in anuplink subframe. A base station 60 receives first data transmitted by afirst mobile station 62. A relay station 61 relays second data to thebase station 60. At this time, a second mobile station 63 is not allowedto transmit data to the relay station 61. This can be implemented insuch a manner that the base station 60 (or the relay station 61) doesnot perform uplink scheduling for the second mobile station 63 in acorresponding subframe. Meanwhile, the data transmitted by the relaystation 61 and the data transmitted by the first mobile station 62 canuse at least any one of different resources (e.g., differentfrequencies, different codes, and different times).

FIG. 8 is a diagram showing another example of the transmission of datain an uplink subframe. A base station 70 receives first data from afirst mobile station 72. A relay station 71 receives second datatransmitted by a second mobile station 73.

FIG. 9 is a diagram showing the transmission of data in a swappedsubframe. A relay station 81 receives first data transmitted by a secondmobile station 83 and at the same time receives second data transmittedby a base station 80. At this time, the second mobile station 83 cantransmit the first data using resources (e.g., time division, codedivision, and frequency division) which do not overlap with resourcesthat are used by the base station 80 to transmit the second data to therelay station 81. The base station 80 does not receive a signaltransmitted by a first mobile station 82. This can be implemented insuch a manner that the base station 80 does not perform uplinkscheduling for the first mobile station 82 in a corresponding subframe.

In order to more effectively use a swapped subframe, a base station cancontrol its transmission power when transmitting data to a relay stationin the swapped subframe. In general, the transmission power of a basestation is much stronger than the transmission power of a mobilestation. Thus, if the transmission power is not controlled, datatransmitted from the mobile station to a relay station can be subject tosevere interference due to the transmission power of the base station.

FIG. 10 is a diagram showing the data relay method according to theembodiment of the present invention in the uplink-downlink configuration0. At step S310, in an uplink subframe #2, a relay station transmitsdata to a base station. At this time, the relay station cannot receivedata transmitted by mobile stations. This can be implemented in such amanner that the relay station does not perform uplink scheduling for themobile stations.

At step S320, in an uplink subframe #3 (i.e., a swapped subframe), therelay station receive uplink data from the mobile stations and downlinkdata from the base station. The uplink data and the downlink data can bereceived through different resources.

At step S330, in an uplink subframe #4, the relay station receives datatransmitted by the mobile stations.

At step S340, in an uplink subframe #7, the relay station transmits datato the base station. At step S350, in an uplink subframe #8 (i.e., aswapped subframe), the relay station receives data transmitted by themobile stations and at the same time receives data transmitted by thebase station. At step S360, in an uplink subframe #9, the relay stationreceives data transmitted by the mobile station.

FIG. 11 is a diagram showing the data relay method according to theembodiment of the present invention in the uplink-downlink configuration2. At step S410, in an uplink subframe #2, a relay station transmitsdata to a base station. At this time, the relay station cannot receivedata transmitted by mobile stations. This can be implemented in such amanner that the relay station does not perform uplink scheduling for themobile stations.

At step S420, in an uplink subframe #7 (i.e., a swapped subframe), therelay station receives uplink data from the mobile stations and downlinkdata from the base station. The uplink data and the downlink data can bereceived through different resources.

FIG. 12 is a diagram showing the data relay method according to theembodiment of the present invention in the uplink-downlink configuration3. At step S510, in an uplink subframe #2, a relay station transmitsdata to a base station. At this time, the relay station cannot receivedata transmitted by mobile stations. This can be implemented in such amanner that the relay station does not perform uplink scheduling for themobile stations.

At step S520, in an uplink subframe #3 (i.e., a swapped subframe), therelay station receives uplink data from the mobile stations and downlinkdata from the base station. The uplink data and the downlink data can bereceived through different resources. At step S530, in an uplinksubframe #4 (i.e., a swapped subframe), the relay station receivesuplink data from the mobile stations and downlink data from the basestation. This method illustrates that two consecutive swapped subframesmay exist in one radio frame.

FIG. 13 is a diagram showing the data relay method according to theembodiment of the present invention in the uplink-downlink configuration4. At step S610, in an uplink subframe #2, a relay station transmitsdata to a base station. At this time, the relay station cannot receivedata transmitted by mobile stations. This can be implemented in such amanner that the relay station does not perform uplink scheduling for themobile stations.

At step S620, in an uplink subframe #3 (i.e., a swapped subframe), therelay station receives uplink data from the mobile stations and downlinkdata from the base station. The uplink data and the downlink data can bereceived through different resources.

FIG. 14 is a diagram showing the data relay method according to theembodiment of the present invention in the uplink-downlink configuration5. At step S710, in an uplink subframe #2 (i.e., a swapped subframe), arelay station receives uplink data from mobile stations and downlinkdata from a base station. The uplink data and the downlink data can bereceived through different resources. In the uplink-downlinkconfiguration 5, the uplink transmission of the mobile station can beperformed by dynamically setting the uplink subframe of a previous ornext radio frame as a swapped subframe because an opportunity for theuplink transmission is fewer than that in other uplink-downlinkconfigurations.

FIG. 15 is a diagram showing the data relay method according to theembodiment of the present invention in the uplink-downlink configuration6. At step S810, in an uplink subframe #2, a relay station receivesuplink data from mobile stations. At step S820, in an uplink subframe#3, the relay station relays the uplink data to the base station. Atstep S830, in an uplink subframe #4 (i.e., a swapped subframe), therelay station receives uplink data from the mobile stations and downlinkdata from the base station.

FIG. 16 is a block diagram of a relay station according to an embodimentof the present invention. A relay station 900 includes a transceiver 910and a processor 920. The transceiver 910 receives data from a basestation (or a mobile station) and also relays the data to a mobilestation (or a base station). The processor 920 functions to process andrelay data received from the transmitter/receiver 910. Theabove-described data relay method can be implemented by the processor920.

The present invention can be implemented using hardware, software, or acombination of them. In the hardware implementations, the presentinvention can be implemented using an Application Specific IntegratedCircuit (ASIC), a Digital Signal Processor (DSP), a Programmable LogicDevice (PLD), a Field Programmable Gate Array (FPGA), a processor, acontroller, a microprocessor, other electronic unit, or a combination ofthem, which is designed to perform the above-described functions. In thesoftware implementations, the present invention can be implemented usinga module that performs the above-described functions. The software canbe stored in a memory unit and executed by a processor. The memory unitor the processor can use various means that are well known to thoseskilled in the art.

Although some embodiments of the present invention have been describedabove, those having ordinary skill in the art will appreciate that thepresent invention may be modified in various forms without departingfrom the spirit and scope of the present invention defined in theappended claims. Accordingly, a possible change of the embodiments ofthe present invention may not deviate from the technology of the presentinvention.

1. A method of relaying data in a wireless communication system based onTime Division Duplex (TDD) using a radio frame comprising a plurality ofsubframes, the plurality of subframes comprising at least one downlinksubframe and at least one uplink subframe, the method comprising:receiving downlink data from a base station in an uplink subframe; andrelaying the downlink data to at least one mobile station.
 2. The methodof claim 1, further comprising receiving uplink data from a mobilestation in the uplink subframe.
 3. The method of claim 2, whereinresources used by the base station to transmit the downlink data in theuplink subframe and resources used by the mobile station to transmit theuplink data do not overlap with each other.
 4. The method of claim 3,wherein the resources are subject to time division or frequencydivision.
 5. The method of claim 1, further comprising receivinginformation about the uplink subframe in which the downlink data isreceived.
 6. The method of claim 1, further comprising selecting theuplink subframe in which the downlink data is received from among theplurality of uplink subframes.
 7. The method of claim 1, wherein theradio frame comprises 10 subframes.
 8. The method of claim 7, whereinthe radio frame corresponds to at least any one of configurations inTable 1 below, wherein ‘D’ denotes a downlink subframe, ‘U’ denotes anuplink subframe, and ‘S’ denotes a special subframe. UPLINK- DOWNLINKSUBFRAME NUMBER CONFIGURATION 0 1 2 3 4 5 6 7 8 9 0 D S U U U D S U U U1 D S U U D D S U U D 2 D S U D D D S U D D 3 D S U U U D D D D D 4 D SU U D D D D D D 5 D S U D D D D D D D 6 D S U U U D S U U D


9. A relay station in a wireless communication system based on TDD usinga radio frame comprising a plurality of subframes, the plurality ofsubframes comprising at least one downlink subframe and at least oneuplink subframe, the relay station comprising: a transceiver configuredto transmit or receive a radio signal; and a processor coupled to thetransceiver and configured to process downlink data received from a basestation and relay the downlink data to a mobile station, wherein theprocessor receives the downlink data from the base station in at leastany one of the uplink subframes included in the radio frame.